1. Field of the Invention
This invention pertains to the implantation of light emitting devices into a tumor or other tissue body for treatment using light energy. More particularly this invention relates to a light probe incorporating LEDs or vertical cavity surface emitting lasers (VCSEL) and a structure for improving the placement of such probes in a tissue body. An alignment grid may be used to facilitate accurate placement of the light probe within the tissue body. Medical diagnostic situations and PDT treatment are environments which the present invention may be utilized. Photodynamic therapy (PDT) is a medical technology which uses light energy in combination with photosensitizing agents to treat or detect pathologies of living tissue, including cancer and microbiological pathogens. Once pre-sensitized by the photosensitizing agent, the cancerous or abnormal cells can be destroyed by irradiation with light of an appropriate wavelength or waveband corresponding to an absorbing wavelength of the agent, with less damage to normal tissue. This procedure has been clinically used to treat a variety of cancers and tumors. Because PDT may be selective in destroying abnormal cells that have absorbed more of the agent, it can successfully be used to destroy malignant tissue with less effect on surrounding benign tissue in the brain and other critical areas.
2. Brief Discussion of the Prior Art
Photodynamic therapy is a modality that involves the use of a photosensitizing agent and a specific wavelength of light to create oxygen radicals, resulting in the destruction of cancer cells, bacteria, viruses, or fungi. A PDT system consists of three principal components: a photosensitizing agent, a light source (typically a laser), and a light delivery means (typically optical fiber based). Two principal challenges for this emerging field of medicine are the development and validation of photosensitizer agents, and the development of reliable wavelength specific (laser) light sources at appropriate and convenient energy levels.
PDT entails the use of a photosensitizing agent that is relatively selectively concentrated in cancer cells or microbiological pathogen sites. Depending on the type of photosensitizer, it may be injected intravenously, ingested orally, or applied topically. After application of the photosensitizer, it is selectively retained by diseased tissue so that after a period of time, determined by the kinetics of the compound's distribution, there is more photosensitizer in the diseased tissue than in the normal tissue. The photosensitizer is then activated with a specific wavelength of light matching the absorption characteristics of the specific photosensitizer, typically using a laser. This results in tissue necrosis via several mechanisms including oxygen radical production as well as vascular shutdown to the diseased tissue. Because there is less photosensitizer in the adjacent normal tissue, only the diseased tissue necroses and the normal tissue is preserved when the correct light dose rate for that tissue is administered. The advantage of PDT over the other conventional modalities of surgery, radiation and chemotherapy is its relatively selective destruction of diseased tissue with normal tissue preservation.
One prior method of delivery of the light energy to the tissue site is by remote illumination through single or multiple optical fibers. The use of optical fibers allow for ease of manipulation and electrical isolation, important criteria in the surgical arena, as well as the possibility of delivery within the body by an endoscopic apparatus. The beam is typically modified by optical accessories on the distal end of the fiber optic cable to direct the energy in a manner appropriate to the treatment requirements. Limitations of the remote illumination of tissue from an optical fiber include irregular illumination and difficulty in obtaining consistent light dosage through out the tissue body (due to light absorbtion of the tissue).